Radio transmission control method, radio receiver apparatus, and radio transmitter apparatus

ABSTRACT

Conventionally, if the number of transmission antennas is greater than that of reception antennas, different signals simultaneously transmitted from the transmission antennas cannot be separated from one another at the receiving end, resulting in a significant degradation of received-signal quality. A transmitter and a receiver each have a plurality of antennas. The transmitter transmits a pilot signal. The receiver receives the pilot signal, calculates transmission-related information corresponding to the pilot signal, selects, based on this calculated information, a transmission signal to be used by the transmitter, and notifies the transmitter of the selected signal. The transmitter selects, from the informed transmission signal, transmission antennas and uses the selected antennas to transmit information signals, so that a signal separation can be easily performed at the receiving end.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional application of and claims thebenefit of priority under 35 U.S.C. §120 from U.S. application Ser. No.10/567,339, filed Nov. 30, 2006, the entire contents of which isincorporated herein by reference. U. S. application Ser. No. 10/567,339is a national stage of International Application No. PCT/JP04/10845,filed Jul. 29, 2004, which is based upon and claims the benefit of priorJapanese Patent Application No. 2003-286184, filed Aug. 4, 2003.

TECHNICAL FIELD

The present invention relates to a radio transmission control method fora MIMO system in which a radio receiver apparatus and a radiotransmitter apparatus respectively use a plurality of antennas toperform SDM transmission, and a radio receiver apparatus and a radiotransmitter apparatus.

BACKGROUND ART

Recently, radio communications has come into widespread use remarkablyowing to its convenience. As a result, there is an urgent demand fortaking measures to deal with the shortage of use frequencies. As one ofthe techniques of using the use frequency effectively, there is a MIMO(Multiple-Input Multiple-Output) system for performing high-speed signaltransmission using a plurality of antennas in a transmitter/receiver,which is under active studies. In the MIMO system, it is known that ahigher capacity can be achieved by using a plurality of antennas in atransmitter/receiver, compared with the case where thetransmitter/receiver has one antenna.

In the MIMO system, SDM (Space Division Multiplexing) transmission hasbeen mostly studied, in which signals are sent individually from aplurality of transmission antennas, and each signal is extracted withsignal processing on a receiving side. Hereinafter, a conventionaltechnique will be described based on representative documents (forexample, see Non-Patent Documents 1 and 2) related to the SDMtransmission.

FIGS. 32 and 33 show a configuration of a transmitter/receiverperforming the SDM transmission. In the SDM transmission, time-seriessignals are sent individually from respective antennas of a transmitter,and as shown in FIG. 33, a receiver receives the signals using beamformation corresponding to each transmission signal. A configuration ofthis signal processing will be described below. The description will bemade assuming that the number of transmission antenna is N, the numberof reception antennas is M, the channel gain from a transmission antennan to a reception antenna m is h_(mn), and the propagationcharacteristics between the transmitter and the receiver is a matrixH=[h_(mn)].

As shown in FIG. 32, at a terminal A1 of the transmitter, time-seriestransmission signals s_(n)(p) (n=1, . . . , N) are transmitted from Ntransmission antennas 3. The transmission signals pass through apropagation path 5 to be received by M reception antennas 4. At aterminal B2 of the receiver, reception weight multiplying parts 131,132, 133 multiply the reception signals with a weight v_(m) to therebyperform signal combining.

Hereinafter, the above-mentioned series of processes will be shown usingmathematical expressions. Assuming that a reception signal at thereception antenna 4 is x_(m)(p), a reception vector x(p)=[x₁(p), . . . ,x_(m)(p)]^(T) (T is a transposition) is given by the followingexpression.x(p)=Σ_(n=1) ^(N) h _(n) s _(n)(p)+z(p)

Herein, s₁(p), . . . , s_(N)(p) represents a transmission signal;h_(n)=[h_(1n), . . . , h_(Mn)]^(T) represents a propagation vector fromthe transmission antenna 3 to the M reception antennas 4; z (p)=[z₁(p),. . . , z_(M)(p)]^(T) represents a noise and interference vector; andz_(m)(p) represents a noise and interference component at the antenna 4.

Furthermore, the terminal B2 on the receiving side determines a weightv_(n)=[v_(n1), . . . , v_(nM)]^(T) suitable for receiving the signals_(n)(p) from the transmission antenna 3. An output y_(n)(p) after thesignal combining is given by the following expression.y _(n)(p)=v _(n) ^(T) x(p)=Σ_(n0=1) ^(N)(v _(n) ^(T) h _(n0))s_(n0)(p)+v _(n) ^(T) z(p)

Although there are various methods for determining the reception weightv_(n), each reception weight v_(n) is determined to get the transmissionsignal s_(n)(p). For example, according to the weight determinationbased on a ZF (Zero Forcing) standard, the weight v_(n) is determined soas to satisfy the following expressions.v _(n) ^(T) h _(n0)=1 where n0=n.v _(n) ^(T) h _(n0)=0 where n0 is other than n.  (Expression 1)

(Expression 1) shows the condition under which a desired signal s_(n)(p)is received strongly, and the other signals s_(n0)(p) (n0 is an integerother than n) are suppressed. Thus, only the desired signal can bereceived satisfactorily. Furthermore, by receiving a signal usingdifferent weights v_(n) with respect to different n, a plurality ofsignals can be separated to be taken out, and hence, divisionmultiplexing can be performed spatially. Herein, although a method fordetermining a weight based of the ZF standard has been described as anexample, there is also a similar weight algorithm such as an MMSEsynthesis method. The purpose of any weight algorithm is basically tosuppress signals other than a desired one in the same way as in(Expression 1).

Thus, by suppressing signals other than a desired one among a pluralityof signals at the terminal B2 on the receiving side, SDM (Space DivisionMultiplexing) can be realized. In the SDM transmission, a plurality ofsignals are transmitted simultaneously, so there is an advantage thathigh-speed signal transmission can be performed, compared with aconventional transmission system in which a transmitter/receiver uses asingle antenna.

However, actually, although (Expression 1) can be realized in the casewhere the number N of multiplexed signals is M or less (N≦M), it cannotbe realized in the case of N>M. In order to understand the contentsthereof, more detailed description will be made. In (Expression 1), thevectors v_(n) and h_(n0) can be respectively expressed as one vector onan M-dimensional space. Furthermore, v_(n) ^(T)h_(n0) being a vectorinner product, and v_(n) ^(T)h_(no) being 0 correspond to a state wherev_(n) and h_(n0) are orthogonal to each other on the M-dimensionalspace. Although one vector v_(n) orthogonal to (M−1) independent vectorsh_(n0) can be set on the M-dimensional space, it is impossible to set avector v_(n) orthogonal to M or more independent vectors h_(n0). Thus,it is theoretically impossible to satisfy the relationship v_(n)^(T)h_(n0)=0 with respect to M or more independent vectors h_(n0), and(Expression 1) does not hold for N>M.

Accordingly, in the case where the number N of multiplexed signals islarger than the number M of reception antennas, any weight v_(n) used onthe receiving side cannot suppress other signals sufficiently.Therefore, the quality of a reception signal degrades rapidly. In orderto avoid this situation, there is required a method of performing spacedivision multiplexing transmission smoothly in an environment where thenumber of transmission antennas is larger than the number of receptionantennas. However, such solution measures have not been introduced asyet.

-   Non-Patent Document 1: A. V. Zelst, R. V. Nee, and G. A. Awater,    “Space Division Multiplexing (SDM) for OFDM systems” IEEE Proc. of    VTC 2000 Spring, pp. 1070 to 1074, 2000-   Non-Patent Document 2: Kurosaki, Asai, Sugiyama, Umehira, “100    Mbit/s. SDM-COFDM over MIMO channel for broadband mobile    communications” Technical Report, RCS 2001-135, October 2001

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention

According to a beam formation method of a conventional procedure, in thecase where the number of transmission antennas is smaller than thenumber of reception antennas, Space Division Multiplexing can beperformed smoothly. However, in actual radio communication, there are anumber of environments where the number of transmission antennas islarger than the number of reception antennas. In such a case, whendifferent signals are sent simultaneously from respective transmissionantennas using a conventional transmission method, the signals cannot beseparated from one another on a receiving side, which greatly degradesthe quality of the reception signals. Thus, there is a demand for amethod capable of separating signals from one another and transmitting asignal of high quality in an environment where the number oftransmission antennas is larger than the number of reception antennas.

Furthermore, a method of sending signals using all the transmissionantennas does not necessarily have a satisfactory transmissionefficiency even in the case where the number of transmission antennas issmaller than the number of reception antennas. For example, in the casewhere two propagation vectors h_(n0) and h_(n1) are similar to eachother, suppressing one signal h_(n1) may also suppress the desiredsignal h_(n0). In such a case, it may be better to stop one of thesignals, rather than to send both signals, for performing signaltransmission more satisfactory.

Thus, controlling a procedure for sending signals raises the possibilityof attaining more efficient signal transmission. There is a demand for acontrol method and a communication system between a transmitter and areceiver, enabling more efficient signal transmission over the MIMOsystem.

Means for Solving the Problem

According to an aspect of this disclosure, there is provided a radiocommunication method for a radio communication system in which outputsignals are generated from a plurality of information signals and thentransmitted to a system of a communication partner from a plurality ofantennas. The method includes receiving control information transmittedby the system of the communication partner and determining, based on thereceived control information, a first weight corresponding to theplurality of antennas for one of the plurality of information signalsmodulated by a first modulation scheme and encoded by a first encodingmethod, and a second weight corresponding to the plurality of antennasfor another one of the plurality of information signals modulated by asecond modulation scheme and encoded by a second encoding method. Afirst operation result is generated by multiplying the one of theplurality of information signals by the first weight, and a secondoperation result is generated by multiplying the another one of theplurality of information signals by the second weight. Based on thefirst operation result and the second operation result, a plurality ofthe output signals are generated, where each corresponds to one of theplurality of antennas. The plurality of the output signals aretransmitted to the system of the communication partner. The controlinformation includes information on the first and second weights andtransmission format information, on modulation scheme and encodingmethod, corresponding to the information on the first and secondweights. The modulation scheme and the encoding method correspond to thetransmission format information, which is determined based on a signalquality calculated on the assumption that the output signals of theplurality of antennas are generated utilizing the weights correspondingto the information on the first and second weights and transmittedsimultaneously.

Further, according to another aspect of this disclosure, there isprovided a radio communication system in which output signals aregenerated from a plurality of information signals and then transmittedto a system of a communication partner from a plurality of antennas. Thesystem includes a reception device for receiving control informationtransmitted by the system of the communication partner and a weightdetermining device for determining, based on the received controlinformation, a first weight corresponding to the plurality of antennasfor one of the plurality of information signals modulated by a firstmodulation scheme and encoded by a first encoding method, and a secondweight corresponding to the plurality of antennas for another one of theplurality of information signals modulated by a second modulation schemeand encoded by a second encoding method. The system further includes anoperation device for generating a first operation result by multiplyingthe one of the plurality of information signals by the first weight, andgenerating a second operation result by multiplying the another one ofthe plurality of information signals by the second weigh. A transmissiondevice is also provided which generates, based on the first operationresult and the second operation result, a plurality of the outputsignals each corresponding to one of the plurality of antennas, andtransmits the plurality of the output signals to the system of thecommunication partner. The control information includes information onthe first and second weights and transmission format information, onmodulation scheme and encoding method, corresponding to the information.The modulation scheme and encoding method correspond to the transmissionformat information being determined based on the signal qualitycalculated on the assumption the output signals of the plurality ofantennas are generated utilizing the weights corresponding to theinformation and transmitted simultaneously.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 A basic structural view of a transmitter/receiver for a MIMOsystem in Embodiment 1 of the present invention.

FIG. 2 A flowchart showing a transmission control method in Embodiment1.

FIG. 3 A view showing a situation in which a control signal istransmitted from a terminal B to a terminal A in Embodiment 1.

FIG. 4 A view showing a situation in which an information signal istransmitted from the terminal A to the terminal B in Embodiment 1.

FIG. 5 A format view of a pilot signal and a control signal used inEmbodiment 1.

FIG. 6 A structural view of a pilot signal detecting part of theterminal B in Embodiment 1.

FIG. 7 A schematic view of a transmission signal determining part inEmbodiment 2.

FIG. 8 A flowchart showing a processing procedure in the transmissionsignal determining part in Embodiment 2.

FIG. 9 A schematic view of a transmission signal determining part inEmbodiment 3.

FIG. 10 A flowchart showing a processing procedure in the transmissionsignal determining part in Embodiment 3.

FIG. 11 A schematic view of a transmission signal determining part inEmbodiment 4.

FIG. 12 A flowchart showing a processing procedure in the transmissionsignal determining part in Embodiment 4.

FIG. 13 A view showing an SINR prediction method in Embodiment 4.

FIG. 14 A view of a table showing a relationship between an output SINRand an evaluation value in Embodiment 4.

FIG. 15 A view of a table showing a correspondence between a combinationof signals and an evaluation value in Embodiment 4.

FIG. 16 A flowchart showing a control procedure in the transmissionsignal determining part in Embodiment 4.

FIG. 17 A view of a table showing a relationship among an output SINR, atransmission format, and an evaluation value in Embodiment 5.

FIG. 18 A view of a table showing a relationship between an output SINRand an evaluation value in Embodiment 5.

FIG. 19 A view showing an example of a format of a control signal usedin Embodiment 5.

FIG. 20 A basic structural view of a multi-carrier communication system.

FIG. 21 A structural view of a transmitter/receiver of multi-carrier SDMtransmission in Embodiment 6.

FIG. 22 A configuration view of a configuration of a transmission signaldetermining part in Embodiment 7.

FIG. 23 A flowchart showing a processing procedure in the transmissionsignal determining part in Embodiment 7.

FIG. 24 A view of a calculation method of an average output SINR inEmbodiment 7.

FIG. 25 A basic structural view of a transmitter/receiver for a MIMOsystem in Embodiment 8.

FIG. 26 A flowchart showing a transmission control method in Embodiment8.

FIG. 27 A conceptual view of a transmitter/receiver for a MIMO system inEmbodiment 9.

FIG. 28 A flowchart showing a transmission control method in Embodiment9.

FIG. 29 A view of a table showing a correspondence between a combinationof signal powers and an evaluation value in Embodiment 10.

FIG. 30 A flowchart showing a processing procedure in the transmissionsignal determining part in Embodiment 10.

FIG. 31 A view showing one example of a format of a control signal usedin Embodiment 10.

FIG. 32 A structural view of a transmitter/receiver during SDMAtransmission according to prior art.

FIG. 33 A conceptual view of a transmitter/receiver configuration, andof reception beam formation during SDMA transmission according to priorart.

BEST MODES FOR CARRYING OUT THE INVENTION

Hereinafter, each embodiment of the present invention will be describedwith reference to the drawings.

Embodiment 1

This embodiment relates to an efficient signal transmission method andcommunication system in a MIMO system in which a plurality of signalsare subjected to space division multiplexing (SDM) transmission. In thefollowing description, a transmitting side of an information signal willbe referred to as a terminal A, and a receiving side thereof will bereferred to as a terminal B.

FIG. 1 is a most basic transmission/reception structural view showingthis embodiment. FIG. 2 is a flowchart showing a control procedure ofthis embodiment. FIG. 3 shows how the terminal B notifies the terminal Aof a control signal (control information). FIG. 4 shows how the terminalA transmits an information signal to the terminal B. In FIG. 5, (a)represents a pilot signal sent from the terminal A, and (b) represents acontrol signal transmitted from the terminal B to the terminal A. FIG. 6shows a configuration of a pilot signal detecting part at the terminalB. Hereinafter, this embodiment will be described with reference toFIGS. 1 to 6.

This embodiment relates to a high efficient signal transmission methodthat is applicable to a MIMO system irrespective of the number oftransmission/reception antennas in the system.

Referring to FIG. 2, a basic control procedure of this embodiment willbe described. First, in this embodiment, the terminal A sends a pilotsignal from each antenna 3 before sending an information signal (S101).When receiving the pilot signals, the terminal B estimates a propagationvector of each pilot signal as transmission-related information (S102).Although there are various specific methods of estimating a propagationvector, a specific example thereof will be described later. The terminalB determines, based on the estimated propagation vector, a transmissionsignal (transmission channel) to be used for sending an informationsignal (S103), and notifies the terminal A of the transmission signal tobe used with a control signal (S104). When receiving the control signal,the terminal A selects the antenna 3 to be used based on thetransmission signal to be used, and sends an information signal to theterminal B (S105).

By performing control in accordance with such a procedure, atransmission antenna can be selected in accordance with a propagationenvironment, and efficient signal transmission can be performed. Thisembodiment is applicable to any cases irrespective of thetransmission/reception antennas. Particularly, in the case where thenumber N of the transmission antennas is larger than the number M of thereception antennas, by reducing the number of the transmission antennasused for sending, the information signal can smoothly be separated andreceived at the terminal B.

FIG. 1 shows a transmitter/receiver configuration in this control. Inthe figure, the terminal A1 (radio transmitter apparatus) includes asignal sending part 6, a control information receiving part 7, and atransmission signal determining part 8. On the other hand, the terminalB2 (radio receiver apparatus) includes a pilot signal detecting part 9,a transmission signal determining part 10, a control informationtransmitting part 11, and an information signal receiving part 12.

Furthermore, the terminal A1 includes N antennas 3, and the terminal B2includes M antennas 4. The propagation characteristics of a propagationpath 5 between a transmitter and a receiver are represented as a matrixH=[h_(mn)].

An operation of this embodiment will be described in detail withreference to FIGS. 1 and 2. The signal sending part 6 of the terminal A1sends a pilot signal from each antenna 3 before sending an informationsignal (S101). The pilot signal detecting part 9 of the terminal Bdetects (i.e., receives) the pilot signals from the terminal A throughthe antennas 4, and estimates a propagation vector of each pilot signal(S102). Although there are various specific methods of estimating apropagation vector, a specific example thereof will be described later.The transmission signal determining part 10 judges (i.e., determines) atransmission signal to be used for sending an information signal basedon the estimated propagation vector. In this embodiment, a combinationof transmission signals used for transmitting an information signal isdetermined (S103). The control information transmitting part 11 notifiesthe terminal A of the determined combination of transmission signalsthrough the antennas 4 with a control signal (S104). FIG. 3 showstransmission of a control signal from the terminal B2 to the terminalA1. The terminal A1 receives the control signal from the terminal B2through the antennas 3 at the control information receiving part 7, andthe transmission signal determining part 8 determines a transmissionsignal to be used, based on the control signal, i.e., selects theantenna 3 to be used. After this, as shown in FIG. 4, the signal sendingpart 6 of the terminal A1 sends an information signal from the selectedantenna 3 (S105), and the terminal B receives an information signal atthe information signal receiving part 12.

In FIG. 5, (a) represents a pilot signal 20 of this control, and (b)represents an example of each format of the control signal 21. Theterminal A sends pilot signals s_(n)(p), which are different from oneanother, from each antenna 3. Furthermore, in the control signal fromthe terminal B to the terminal A, the terminal A is notified of “1” inthe case where transmission is performed with respect to antennasnumbered #1 to #N, and notified of “0” in the case where transmission isnot performed. Various types of signal formats are considered, and thisformat is merely an example. Any signal format may be used, as long asit is a pilot signal that can be used for estimating a propagationvector or a control signal that can notify the terminal A of atransmission signal to be used.

FIG. 6 shows a configuration of estimating a propagation vector at thepilot signal detecting part 9 of the terminal B. The estimation of apropagation vector can be performed by obtaining a correlation betweenthe received pilot signal and the known pilot signal s_(n)(p) previouslystored in the pilot signal detecting part 9 for each antenna.

More specifically, a propagation vector h_(n)=[h₁₁, h₂₁, . . .h_(M1)]^(T) can be estimated by the following expression with respect toa reception vector x(p)=[x₁(p), . . . , x_(M)(p)]^(T).h _(n)=Σ_(n=1) ^(N) s(p)s _(n)(p)*

Herein, * represents a complex conjugate. Generally, this operation isrealized using an MF (Matched Filter). Although FIG. 6 shows an examplein which a propagation vector is estimated, any configuration other thanthis may be used, as long as propagation information that istransmission-related information regarding a reception signal to a pilotsignal is detected. Furthermore, any parameter other than a propagationvector may be used, as long as the parameter serves as effectivepropagation information regarding a pilot signal.

When the pilot signal detecting part 9 calculates propagationinformation (estimation of a propagation vector), the transmissionsignal determining part 10 selects a transmission signal using theinformation. Various methods of selecting a transmission signal areconsidered. Hereinafter, in Embodiments 2 to 5, some examples will beshown regarding the method of selecting a transmission signal. Thepresent invention is not limited to examples of a selection methoddescribed in Embodiments 2 to 5, and any selection method may be used aslong as the transmission of an information signal is controlled usingpropagation information that is transmission-related information,whereby the efficiency of transmission is enhanced.

Embodiment 2

This embodiment relates to an efficient transmission control method andcommunication system for a MIMO system in which a plurality of signalsare subjected to space division multiplexing (SDM) transmission. Inparticular, this embodiment shows one specific method regarding a methodof selecting a transmission signal for the terminal B in Embodiment 1.

FIG. 7 shows a transmission signal determining part 10 in thisembodiment. FIG. 8 is a flowchart showing a control procedure in thetransmission signal determining part 10. Hereinafter, a method ofselecting a transmission signal in this embodiment will be describedwith reference to FIGS. 7 and 8.

As shown in FIG. 7, the transmission signal determining part 10 selectsR signals having power as large as possible from among a plurality oftransmission signals. Specifically, when received a propagation vectorh_(n) from the pilot signal detecting part 9, the transmission signaldetermining part 10 of the terminal B selects R signals in a decreasingorder of norm ∥h_(n)∥ (S201). Then, the transmission signal determiningpart 10 notifies the control information transmitting part 11 of numbersn of the selected signals (S202).

According to the above selection, a channel having a satisfactorypropagation environment can be selected to be used. Furthermore, bysetting the number R of signals to be selected to be smaller than thenumber M of reception antennas, each information signal can also beseparated and received at the terminal B.

Thus, according to this embodiment, a transmission signal (transmissionchannel) having a satisfactory propagation environment is selected toperform signal transmission. Furthermore, each information signal cansmoothly be separated and received at the receiver.

Embodiment 3

This embodiment relates to an efficient transmission control method andcommunication system for a MIMO system in which a plurality of signalsare subjected to space division multiplexing (SDM) transmission. Inparticular, this embodiment relates to one method regarding a method ofselecting a transmission signal at the terminal B in Embodiment 1, whichis different from that of Embodiment 2.

FIG. 9 shows a transmission signal determining part 10 in thisembodiment, and FIG. 10 is a flowchart showing a control procedure inthe transmission signal determining part 10. Hereinafter, a method ofselecting a transmission signal in this embodiment will be describedwith reference to FIGS. 9 and 10.

As shown in FIG. 9, the transmission signal determining part 10 selectsR signals from among a plurality of transmission signals such that thespatial correlation becomes as small as possible. Herein, the spatialcorrelation refers to a parameter defined by|h _(n1) ^(H) h _(n2)|/(∥h _(n1) ∥∥h _(n2)∥) or |h _(n1) ^(H) h _(n2)|,andas this parameter is smaller, signals n1, n2 are in a state close to aspatially orthogonal relationship. As the relationship between thesignals is close to an orthogonal relationship, it is easy to separatetwo signals at the terminal B. According to this selection, signaltransmission can be performed in an environment in which signals arelikely to suppress one another. Accordingly, each information signal caneasily be separated at the terminal B.

As a specific control procedure, when the propagation vector h_(n) isestimated in the pilot signal detecting part 9 of the terminal B, first,the transmission signal determining part 10 selects a signal n at whicha norm ∥h_(n)∥ is maximum (S301). Then, the selected signal n is addedto a group of a variable n1 (S302). In an initial state, the group of n1does not have elements. In a case where the number of elements of thevariable n1 is smaller than R (S303), a signal n at which the sum ofspatial correlation of the signal belonging to the group n1 and thesignal n:Σ_(n1) |h _(n) ^(H) h _(n1)|/(∥h _(n) ∥∥h _(n1)∥)is minimum is newly selected from the group other than the group of thevariable n1 (S305), and the signal n is added to the group n1 as anelement (S302). Furthermore, in a case where the number of elements ofn1 is equal or larger than R at the end of Step S302 (S303), the controlinformation transmitting part 11 is notified of the number selected asthe group n1 (S304), and the processing is completed.

According to such a series of processing, a combination of signalshaving a small spatial correlation can be selected, and each informationsignal can smoothly be separated and received at the terminal B.Accordingly, high-efficient signal transmission can be performed.Furthermore, even in a case where the number N of transmission antennasis larger than the number M of reception antennas, by setting the numberR of signals to be selected to be smaller than the number M of receptionantennas, each information signal can be separated and received at theterminal B.

Embodiment 4

This embodiment relates to an efficient transmission control method andcommunication system in a MIMO system in which a plurality of signalsare subjected to space division multiplexing (SDM) transmission. Inparticular, this embodiment relates to one method of selecting atransmission signal at the terminal B in Embodiment 1, which isdifferent from those of Embodiment 2 and Embodiment 3.

FIG. 11 shows a configuration of the transmission signal determiningpart 10 in this embodiment. FIG. 12 is a flowchart showing a controlprocedure in the transmission signal determining part 10. FIG. 13 showsan example of an SINR prediction method used in this embodiment, andFIG. 14 shows a correspondence table of an SINR for determining anevaluation value and an evaluation value in the transmission signaldetermining part 10. FIG. 15 shows results obtained by calculating anevaluation value with respect to various combinations of signals. Amethod of selecting a transmission signal of this embodiment will bedescribed with reference to FIGS. 11 to 15.

As shown in FIG. 11, the transmission signal determining part 10includes a signal candidate selecting part 31, an output signal tointerference-plus-noise ratio (SINR) calculating part (hereinafter,referred to as an output SINR calculating part) 32, a transmissionevaluating part 33, and a use signal determining part 34.

In the transmission signal determining part 10, first, the signalcandidate selecting part 31 selects a candidate combination oftransmission signals (S401). The output SINR calculating part 32predicts an output SINR at the terminal B obtained in the case ofsending a combination of transmission signals (S402). A specific exampleof a prediction method will be described later. The transmissionevaluating part 33 determines an evaluation value with respect to thecandidate combination of transmission signals from the predicted outputSINR (S403). This evaluation is performed with respect to all variouscandidate combinations of transmission signals (S404). Finally, the usesignal determining part 34 selects a combination of transmission signalswhose evaluation value is highest, and notifies the control informationtransmitting part 11 of the combination (S405).

FIG. 13 shows a method of predicting an output SINR of each signalperformed in Step S402 in the output SINR calculating part 32.

In calculation of the predicted SINR, a reception weight v_(n) is firstcalculated using an estimated propagation vector h_(n).

For example, in the case of a ZF standard and an MMSE synthesisstandard, the reception weight v_(n) is given by the followingexpression.v _(n)=(Σ_(n0) h _(n0) h _(n0) ^(H))⁻¹ h _(n0) (in the case of the ZFstandard)v _(n)=(Σ_(n0) h _(n0) h _(n0) ^(H) +P _(N) I)⁻¹ h _(n0) (in the case ofthe MMSE standard)

By calculating power of a desired signal and an interference noisecomponent with respect to the operated reception weight, an output SINRcan be obtained by the following (Expression 2).Γ_(n) =|h _(n) ^(H) v _(n)(p)|² /{v _(n) ^(H)(Σ_(n0) h _(n0) h _(n0)^(H) +P _(N) I)v _(n) −|h _(n) ^(H) v _(n)(p)|²}  (Expression 2)where P_(N) is noise power, which is a value previously estimated.

The reception weight v_(n) may be a weight operation other than the ZFstandard and the MMSE standard. The SINR prediction expression of(Expression 2) is applicable to any weight v_(n).

When the output SINR is thus obtained, the transmission evaluating part33 determines a transmission evaluation value based on the SINR. Herein,as a specific example, a method of setting an evaluation value to 0 or 1in accordance with the SINR will be described. However, this embodimentis not limited to the transmission evaluating method based on the SINR,and a combination of signals can be selected based on various evaluationstandards.

The present invention is applicable to any MIMO system in which acandidate combination of signals is assumed, transmission evaluation isperformed, and transmission control is performed using results thereof.

The transmission evaluating part 33 has a table for determining anevaluation value with respect to an SINR as shown in FIG. 14. Herein, inthe case where the SINR is 4 dB or more, an evaluation value is set to1, and otherwise, set to 0. This evaluation is executed respectivelywith respect to an output SINR of each signal.

FIG. 15 shows results obtained by performing the above evaluation withrespect to various combinations 51 of signals. In this embodiment,various combinations of signals sent by three antennas are used. Herein,results obtained by performing the prediction of the output SINR 52, thecalculation of the evaluation value 53 of each signal, and thecalculation of the total 54 of the evaluation values (total evaluationvalue) are summarized. Thus, the total 54 of the evaluation values iscalculated with respect to a combination of each signal, and acombination 55 of signals in which the total 54 of the evaluation valuesbecomes maximum in the use signal determining part 34.

In the example shown in FIG. 15, in the case where the antennas #1 and#2 are used, and the antenna #3 is not used, the total of evaluationvalues becomes maximum, and this combination 55 is selected. In the casewhere a plurality of combinations reaching the maximum evaluation valueare present, any one of them is selected. The terminal A is notified ofthe selected combination of signals through the control informationtransmitting part 11.

According to such a control method, a transmission efficiency can beevaluated from various transmission environments, and a combination ofsignals having the most excellent transmission efficiency among them canbe selected. As a result, compared with the conventional MIMO system inwhich transmission control is not performed, a communication systemhaving a high transmission efficiency can be built.

This embodiment can be used for enhancing the transmission efficiencywith respect to any number of transmission/reception antennas. Inparticular, when the number N of transmission antennas is larger thanthe number M of reception antennas, the transmission speed can beimproved while achieving the state where signal division can beperformed at the terminal B, thereby producing a great applicationeffect.

Embodiment 5

This embodiment relates to an efficient transmission control method andcommunication system in a MIMO system in which a plurality of signalsare subjected to Spatial Division Multiplexing (SDM) transmission. Thisembodiment has the same configuration of a transmitter/receiver as thatof Embodiment 1. However, the control signal notified from the terminalB to the terminal A is different, and in this embodiment, a transmissionformat number of each transmission signal is notified.

FIG. 16 shows a flowchart of a control procedure in the transmissionsignal determining part 10 in this embodiment. FIG. 17 is acorrespondence table of an output SINR for determining an evaluationvalue and an evaluation value in the transmission signal determiningpart 10. FIG. 18 shows results obtained by calculating an evaluationvalue with respect to various combinations of signals. FIG. 19 shows anexample of a frame format of a control signals transmitted from theterminal B to the terminal A. Hereinafter, this embodiment will bedescribed with reference to FIGS. 16 to 19.

The transmission signal determining part 10 of this embodiment has theconfiguration in FIG. 11 in the same way as in Embodiment 4, and iscomposed of a signal candidate selecting part 31, an output SINRcalculating part 32, a transmission evaluating part 33, and a use signaldetermining part 34. As a control procedure, first, the signal candidateselecting part 31 selects a candidate combination of transmissionsignals (S501), and the output SINR calculating part 32 predicts anoutput SINR of a signal with respect to the combination (S502). Thetransmission evaluating part 33 determines an evaluation value based onthe results of the output SINR (S503). This evaluation value iscalculated with respect to all various candidate combinations of signals(S504), and finally, a combination of transmission signals having ahighest evaluation value is selected by the use signal determining part34. In this case, the use signal determining part 34 determines atransmission format suitable for sending a combination of signals, andnotifies the control information transmitting part 11 of a transmissionformat number (S505).

FIG. 17 is a table for determining an evaluation value with respect toan output SINR predicted value. This table shows a transmission formatand a transmission speed that realize predetermined communicationquality with respect to the output SINR predicted value. Herein, thepredetermined communication quality refers to a required standardregarding a Bit Error Rate (BER), a Packet Error Rate (PER), or thelike. More specifically, a format such as an encoding method (codingratio, constraint length, etc.) and a modulation scheme is set to causea transmission speed to be as high as possible within a range satisfyingBER or PER of the required standard.

FIG. 17 shows the modulation scheme 63, the coding ratio 64, and thelike to be used under a certain SINR 62. In general, as the SINRincreases, the endurance to a bit error becomes higher, so that a codingratio can be set to be larger. Furthermore, multi-value modulation canalso be used. As a result, the transmission speed 65 increases with theenhancement of the SINR.

By using this table, it is possible to determine a transmission formatfor achieving predetermined required quality under a certain SINR, and atransmission speed thereof. Furthermore, if the transmission speed isused as an evaluation value, an evaluation value can also be calculatedwith respect to various combinations of signals.

FIG. 18 shows results obtained by calculating a total 74 of evaluationvalues, using a transmission speed as an evaluation value 73 of eachsignal with respect to various combinations 71 of signals. The usesignal determining part 34 selects a combination of signals at which thetotal 74 of evaluation values becomes maximum in FIG. 18. In thisembodiment, a combination (1, 1, 0) of signals at which the total ofevaluation values becomes 10.5 is selected.

By selecting a combination at which the total of evaluation valuesbecomes maximum, a transmission speed can be enhanced while a requiredquality standard is being satisfied in a MIMO system.

When a combination of signals is thus selected, a transmission formatnumber is determined with reference to FIG. 17, and the terminal A isnotified of the transmission format number through the controlinformation transmitting part 11. FIG. 19 is an example showing aconfiguration of the control signal 81, and a transmission format numberis specified for each signal. In this figure, “0” represents atransmission format number that is not used as a transmission signal.Furthermore, “8”, “15”, and “6” represent transmission format numberswhen used as transmission signals, and in this embodiment, as shown inFIG. 17, transmission specification numbers “1” to “31” are selected inaccordance with an SINR of each signal of the selected combination.

As described above, the terminal B selects a transmission format numbercorresponding to a combination of transmission signals, and notifies theterminal A of the transmission format number. The terminal A that isnotified of the transmission format number transmits an informationsignal in accordance with a transmission format and a transmission speedcorresponding to the notified transmission format number.

According to this procedure, communication with a higher transmissionspeed can be realized while satisfying required communication quality,compared with the conventional MIMO system in which transmission controlis not performed and the above-mentioned Embodiments 1 to 4. Thus, byadding a degree of freedom to the transmission format, more detailedsystem design can be performed, which can enhance a transmission speed.

In the above description, although a transmission speed is used as anevaluation value, a parameter other than the transmission speed may beused as an evaluation value.

Embodiment 6

This embodiment relates to an efficient transmission control method andcommunication system in a MIMO system in which a plurality of signalsare subjected to space division multiplexing (SDM) transmission. Inparticular, this embodiment shows SDM transmission performingmulti-carrier transmission.

FIG. 20 is a basic structural view illustrating general multi-carriertransmission. FIG. 21 is a structural view of transmission/reception inthe case of applying the MIMO system to multi-carrier transmission.Hereinafter, this embodiment will be described with reference to FIGS.20 and 21.

Recently, in radio communication, there is a great demand for a systemcapable of performing higher-speed transmission and higher-speedmovement, which necessitates broadband radio transmission. Regarding thetransmission of a broadband signal, in particular, attention is beingpaid to a multi-carrier system performing parallel transmission ofsignals simultaneously using a plurality of carriers. According to themulti-carrier transmission system, low-speed data are arranged inparallel on a frequency, and sent simultaneously using differentcarriers. An attempt is made to enhance the transmission speed byperforming parallel transmission of signals.

FIG. 20 is a basic structural view of a multi-carrier communicationsystem. As shown in the figure, in a multi-carrier signal sending part91, a plurality of signals are multiplexed (93 to 96) with a pluralityof different frequencies, whereby signal transmission is performed.Furthermore, in the multi-carrier signal receiving part 92 on areceiving side, signals multiplexed (93 to 96) with a plurality ofdifferent frequencies are separated to obtain a reception signal of eachcarrier. As shown in this figure, the signals multiplexed in themulti-carrier signal sending part 91 are transmitted under the conditionof being multiplexed (93 to 96) with a plurality of frequencies. In thiscase, signals transmitted by each carrier can be dealt withindependently. More specifically, individual signal processing can beperformed for each carrier in the same way as in single-carriertransmission. Thus, in Embodiments 1 to 5, although the case of thesingle-carrier transmission has been described, the similar accesscontrol method can also be applied to the multi-carrier transmissionsystem.

FIG. 21 shows a configuration of signal processing in which the MIMOsystem of the present invention is applied to the multi-carriertransmission system. As shown in this figure, by configuring the MIMOsystem shown in Embodiments 1 to 5 for each carrier, the MIMO system ofthe present invention can be applied to even the multi-carriertransmission system. That is, the terminal A1 includes multi-carriersignal sending parts 101 to 103, and the terminal B2 includesmulti-carrier signal receiving parts 104 to 106.

Embodiment 7

This embodiment shows a transmission control method and a communicationsystem different from those of Embodiment 6, in particular, regardingthe SDM transmission performing multi-carrier transmission.

By performing transmission control independently for each sub-carrier(each carrier) as shown in Embodiment 6, the control similar to that inthe case of a single carrier can be performed. However, when independentcontrol is performed with respect to all the sub-carriers, there is aproblem in that a control amount increases. Then, in this embodiment, amethod of enabling efficient signal transmission in a MIMO system whilereducing a control amount will be described.

FIG. 22 is a structural view of the transmission signal determining part10, and FIG. 23 is a flowchart showing control performed in thetransmission signal determining part 10. FIG. 24 shows an average SINRcalculation method used in the transmission signal determining part 10.Hereinafter, this embodiment will be described with reference to FIGS.22 to 24.

In Embodiment 6, although the evaluation and the selection of a signalare performed for each sub-carrier, in this embodiment, one transmissionevaluation and selection of a signal are performed with respect to allthe sub-carriers. More specifically, an evaluation value with respect toall the sub-carriers is set, and the selection of a transmission signalof all the sub-carriers is performed in accordance with the evaluationvalue. As the evaluation value, various parameters such as averagesignal power, an average spatial correlation, and an average SINR can beused. Herein, the case of using an average SINR will be described as theuse of one of the parameters.

FIG. 22 shows a configuration of the transmission signal determiningpart 10 in the case of performing one transmission evaluation and signalselection with respect to all the sub-carriers. According to thisprocedure, first, the signal candidate selecting part 31 selects acandidate combination of transmission signals (S601), and the averageoutput SINR calculating part 35 predicts an average output SINR (S602).A method of predicating and calculating an average output SINR will bedescribed later. The transmission evaluating part 33 determines anevaluation value with respect to the candidate combination oftransmission signals from the prediction results of an average outputSINR (S603). This evaluation is performed with respect to all variouscombinations of transmission signals (S604), and finally, the use signaldetermining part 34 selects a combination of transmission signals havinga highest evaluation value and notifies the control informationtransmitting part 11 of the combination (S605).

This procedure is configured in the same way as in Embodiment 4, exceptfor using an average output SINR in place of output SINR. Furthermore,by using average signal power, an average spatial correlation, and anaverage SINR, even Embodiments 2, 3, and 5 can be extended to a controlmethod of this embodiment during multi-carrier transmission.

FIG. 24 shows a method of calculating average SINR. Herein, Γ_(n,l) (n:transmission antenna number, l: sub-carrier number) that is an SINR ofeach sub-carrier is calculated in the same way as in Embodiment 4 withrespect to a signal candidate. After this, by averaging an SINR amongsub-carriers, Γ_(n) that is an average SINR with respect to all thesub-carriers is calculated by the following Expression.Γ_(n) =E _(l)[Γ_(n,l])where E_(l)[●] represents performing average regarding l.

In the multi-carrier transmission, encoding/decoding is generallyperformed over a plurality of sub-carriers inmost cases. In this case,the multi-carrier reception characteristics greatly depend upon anaverage SINR, and the transmission characteristics can be substantiallygrasped based on the average SINR. Thus, in the multi-carriertransmission, by using an averaging parameter with respect to all thesub-carriers, efficient signal selection can be performed with a smallcontrol amount.

In this embodiment, a combination of signals to be used is selectedusing an average SINR, and the terminal A is notified of the combinationwith a control signal. In this case, the control signal is common to allthe sub-carriers, and the control amount can be greatly reduced comparedwith Embodiment 6 in which a control method is required for eachsub-carrier.

Embodiment 8

This embodiment shows a method of sending a signal at the terminal A,which is different from Embodiments 1 to 7 in SDM transmission.

In the SDM transmission of Embodiments 1 to 7, the terminal A sends apilot signal and an information signal from each antenna 3. However, theterminal A may not necessarily send a signal individually from eachantenna 3. In this embodiment, the case where the terminal A performstransmission of a pilot signal and an information signal using atransmission beam will be described.

FIG. 25 is a structural view of a transmitter/receiver in thisembodiment. The terminal A1 includes transmission weight calculators111, 112, and 113, and the terminal B2 includes reception weightmultipliers 114, 115, and 116, whereby transmission beams 117, 118, and119 are formed. FIG. 26 is a flowchart showing a control procedure inthis embodiment. Hereinafter, this embodiment will be described withreference to FIGS. 25 and 26.

In this embodiment, the terminal A multiplies a transmission signals_(n)(p) by a weight w_(n)=[w_(n1), w_(n2), . . . , w_(nN)]^(T) toobtain a signal of each antenna 3. In the case where there are aplurality of transmission signals, the terminal A multiplies thetransmission signals by different weights w_(n) to generate signalsindividually for the respective antennas 3, and sends a plurality ofsignals concurrently. In this case, the transmission signals of theterminal A have directivity, whereby transmission beams 117 to 119 areformed. Thus, the terminal A can also send signals from the respectivetransmission beams 117 to 119 instead of the respective antennas 3.

A procedure of transmission control of a MIMO system using transmissionbeam forming will be described with reference to FIG. 26 below. Theterminal A first sends pilot signals from the respective transmissionbeams 117 to 119 (S701). When receiving a pilot signal, the terminal Bestimates a propagation vector of each signal (S702). Furthermore, theterminal B determines a transmission beam to be used based on theestimated propagation vector (S703) and notifies the terminal A of atransmission beam to be used with a control signal (S704). Whenreceiving the control signal, the terminal A selects a transmission beamto be used and sends an information signal to the terminal B (S705).

Thus, even in the case where the terminal A sends a signal using atransmission beam, efficient SDM transmission can be performed owing tothe transmission control between the terminal A and the terminal B,respectively. Similarly, all the procedures of Embodiments 1 to 7 can beextended to the case of using a transmission beam.

The number of transmission beams is not necessarily the same as that ofreception antennas. The number of transmission beams is determined basedon the number of weight multipliers, and can be set to be either largeror smaller than the number of transmission antennas. For example, theterminal A having two antennas 3 can also send four signals using fourtransmission beams.

Embodiment 9

In this embodiment, the application range of the methods of controllingtransmission of Embodiments 1 and 8 can be further extended with respectto SDM transmission.

In Embodiment 8 and Embodiment 1, a method of controlling transmissionhas been stated based on the following premises:

(1) the terminal A transmits a pilot signal from each transmission beam;and

(2) the terminal A transmits a pilot signal from each antenna 3,respectively. However, actually, the terminal B can control transmissioneven without recognizing whether the state is (1) or (2).

FIG. 27 shows a concept of this transmission control method, and FIG. 28shows an example of a flowchart of this embodiment. The terminal A1sends pilot signals 121 and 122 in either state (1) or (2) (S801). Atthis time, the terminal B2 can estimate propagation vectors with respectto the pilot signals even without recognizing either one of (1) and (2)(S802). Furthermore, the terminal B can estimate any of signal power, aspatial correlation, and an output SINR by learning only a series ofpilot signals. Furthermore, the terminal B can also select appropriatesignals corresponding to the pilot signals based on the results (S803).Furthermore, the terminal B can also notify the terminal A of a numberof a transmission signal to be used (S804), thereby notifying theterminal A of the signal to be used. The terminal A having received acontrol signal sends an information signal to the terminal B from anantenna or a transmission beam (S805).

Thus, if the terminal B learns only a series of pilot signals, theterminal B can perform the entire transmission control smoothly evenwhen the terminal A does not recognize any of the states (1) and (2). Asa result, even when the terminal A uses an arbitrary transmission beamor the like irrespective of the terminal B, there arises no problem intransmission control.

From the above results, only a series of pilot signals is determined asa standard previously between terminals, and the use of a transmissionbeam can be subjected to the free determination of each terminal. As aresult, it is not necessary to perform recognition and notification withrespect to the presence/absence of a beam between terminals, and theterminal A can use transmission beam formation with a small controlamount.

Embodiment 10

This embodiment relates to an efficient signal transmission method andcommunication system in a MIMO system in which a plurality of signalsare subjected to space division multiplexing (SDM) transmission.

Unlike the control signal sent from the terminal B to the terminal A inEmbodiment 5, in particular, this embodiment is characterized in thatthe terminal B determines transmission power of each signal, andnotifies the terminal A of the transmission power in addition to atransmission format number.

FIG. 29 shows results obtained by calculating an evaluation value withrespect to various combinations of signals in the transmission signaldetermining part 10. FIG. 30 shows an example of a flowchart of thisembodiment used in the transmission signal determining part 10. FIG. 31is an example of frame format of a control signal 82 transmitted fromthe terminal B to the terminal A. Hereinafter, this embodiment will bedescribed with reference to FIGS. 29 to 31.

The transmission signal determining part 10 of this embodiment has thesame configuration as that shown in FIG. 11, and includes a signalcandidate selecting part 31, an output SINR calculating part 32, atransmission evaluating part 33, and a use signal determining part 34.However, the transmission signal determining part 10 of this embodimentis different from that of the above-mentioned Embodiment 5 in thattransmission power is also transmitted from the terminal B to theterminal A in addition to a transmission format number.

As a control procedure, first, the signal candidate selecting part 31selects a combination 75 of levels of transmission power of each signal(S901), and the output SINR calculating part 32 predicts an output SINR72 at the terminal B (S902). The transmission evaluating part 33calculates an evaluation value (transmission speed) 73 with respect toeach signal from the prediction results of each output SINR 72, and addsup the evaluation values with respect to the respective signals todetermine a total 74 of transmission evaluation values (S903). Thisevaluation is performed with respect to various combinations of levelsof transmission power of signals (S904), and finally, the use signaldetermining part 34 selects a combination of transmission power having ahighest total of evaluation values and notifies the control informationtransmitting part 11 of the combination (S905).

FIG. 29 shows results obtained by predicting the output SINR 72 withrespect to various combinations 75 of levels of signal power, andcalculating an evaluation value. Herein, assuming that the power of aninformation signal is changed with respect to the power of a pilotsignal, the output SINR 72 is predicted. This SINR prediction can beperformed using the same operation method as that of (Expression 2).Furthermore, an evaluation value is determined using the predicted SINR.Thus, by calculating an evaluation value with respect to variouscombinations of levels of power, and selecting a combination having ahighest total evaluation value, transmission power can be optimized. Itshould be noted that a combination of levels of power is created so thatthe total power of transmission signals is within a predetermined range.

Thus, when a combination of levels of power of each signal is selected,the terminal A is notified of a transmission format number of thecombination through the control information transmitting part 11together with the transmission power determined with reference to FIG.17 in the same way as in Embodiment 5. FIG. 31 shows an example showinga configuration of a control signal 82. In FIG. 31, the transmissionpower corresponding to each signal is described in the left column as aratio with respect to the current pilot signal, and the numerical valuein the right column represents a transmission format number. In the itemof power of this control signal, “0” to “3” are defined as the magnitudeof the transmission power when used for a transmission signal, and “0”represents the case where the transmission format number is not used asa transmission signal. Furthermore, regarding the transmission formatnumber, “0” shows that the transmission format number is not used as atransmission signal, and regarding the numbers used as transmissionsignals, transmission specification numbers “1” to “31” are selected inthe same way as in Embodiment 5.

As described above, the terminal B selects a combination of transmissionpower, and notifies the terminal A of the combination. The notifiedterminal A transmits an information signal in accordance with thenotified transmission power and transmission format number.

In Examples 1 to 9, although a change in transmission power of a signalhas not been considered, the power of each transmission signal can beoptimized in this embodiment. As a result, signal transmission can beperformed more efficiently in the MIMO system, considering alsotransmission power.

In this embodiment, although the case of applying a combination of powerto Embodiment 5 has been described, the same procedure can be appliedsimilarly to Embodiments 1 to 9. More specifically, the method ofselecting power using an SINR described in this embodiment is merely onespecific example of the present invention, and various configurations ofa MIMO system, in which the terminal B determines power based onpropagation information and performs transmission control, can be used.

Embodiment 11

This embodiment shows the case where a MIMO system and a CDMA system areused in combination.

When a DS-CDMA system and a multi-carrier CDMA system and a MIMO systemare used in combination, after a code spreaded pilot signal isdespreaded at the terminal B, the procedure similar to those ofEmbodiments 1 to 10 can be applied. Thus, the transmission controlmethods of Embodiments 1 to 10 can also be used in combination with aCDMA system such as the DS-CDMA system and the multi-carrier CDMAsystem.

INDUSTRIAL APPLICABILITY

A receiver selects a transmission method of a signal from a transmitterbased on a pilot signal from the transmitter, and notifies thetransmitter of the transmission method, and the transmitter sends aninformation signal to the receiver in accordance with a signaltransmission method. Therefore, the present invention is applicable to aradio communication device in which signal separation can be performedsmoothly, enhancing a transmission efficiency.

1. A radio communication method by a radio communication system in whichoutput signals are generated from a plurality of information signals andthen transmitted respectively at a plurality of different frequencies toa system of a communication partner from N antennas, the methodcomprising: receiving control information by a control signal which istransmitted by the system of the communication partner; and transmittingtransmission signals respectively at the plurality of frequencies fromthe N antennas based on the received control information, thetransmission signals each being generated based on a first operationresult, which is obtained by multiplying a first information signal by afirst N-dimensional weight vector, and a second operation result, whichis obtained by multiplying a second information signal by a secondN-dimensional weight vector, wherein the control information includesweight-related information representing a set of the first N-dimensionalweight vector and the second N-dimensional weight vector, the firstinformation signal and the second information signal include a set ofsignals modulated and encoded individually, and the weight-relatedinformation is common to all of the plurality of frequencies used forsignal transmission from the radio communication system to the system ofthe communication partner.
 2. A radio communication system in whichoutput signals are generated from a plurality of information signals andthen transmitted respectively at a plurality of different frequencies toa system of a communication partner from N antennas, comprising:reception means for receiving control information by a control signalwhich is transmitted by the system of the communication partner; andtransmission means for transmitting transmission signals respectively atthe plurality of frequencies from the N antennas based on the receivedcontrol information, the transmission signals each being generated basedon a first operation result, which is obtained by multiplying a firstinformation signal by a first N-dimensional weight vector, and a secondoperation result, which is obtained by multiplying a second informationsignal by a second N-dimensional weight vector, wherein the controlinformation includes weight-related information representing a set ofthe first N-dimensional weight vector and the second N-dimensionalweight vector, the first information signal and the second informationsignal include a set of signals modulated and encoded individually, andthe weight-related information is common to all of the plurality offrequencies used for signal transmission from the radio communicationsystem to the system of the communication partner.